The objective of this study is to characterize the pseudoneointima (PNI) formed on the surfaces of blood pumps, both left ventricular assist devices (LVAD) and total artificial hearts (TAH) after various durations in vivo in order to determine the effect of materials, pump components, location on the surface, and duration of pumping. Biolized materials are used for the blood contacting surfaces of the pumps, either chemically treated natural tissue or protein coatings. Anticoagulants are not used with these devices. At termination of all in vivo experiments employing these prostheses, the pumps are carefully removed and the surfaces are chemically preserved for analysis by scanning electron microscopy, histology, and PNI thickness measurements. Having devices used for various lengths of time provides data to determine the PNI development with time on the different surfaces in the pumps. BIBLIOGRAPHIC REFERENCE: The Characterization of Intima Development in Left Ventricular Assist Device (LVAD) and Total Artificial Heart (TAH), G. Picha, M. Helmus, S. Barenberg, D. Gibbons, R. Martin, Y. Nose. Trans. A.S.A.I.O., Volume 22, 1976 (In press).